Women with gestational diabetes mellitus (GDM) have higher rates of foetal macrosomia, shoulder dystocia and pregnancy-induced hypertension, and are at higher risk of developing type 2 diabetes. Herein, we introduce a new conceptual term, "gestational prediabetes", which requires the absence of diabetes before pregnancy, and the presence of blood glucose levels (or a related marker) in early pregnancy that are higher than normal, but not yet high enough to meet the diagnostic criteria for GDM. Identifying women with gestational prediabetes might be done in early pregnancy (e.g., 12 weeks' gestation) using conventional glycaemic testing, assessment of visceral abdominal adiposity or hepatic fat by ultrasonography, or measuring serum sex hormone-binding globulin or adiponectin. However, none of these approaches has been systematically compared to conventional predictors, such as maternal body mass index or waist circumference. Any early-pregnancy predictor of gestational prediabetes risk needs to have low cost, ease of administration, and a short turnaround time. The theoretical advantage of identifying women with gestational prediabetes would be to "prevent" the onset of GDM (and its inherent risks to the pregnancy) in a timelier manner. One sensible starting point would be an intervention to prevent early excessive weight gain in pregnancy, which is currently being evaluated by two randomized clinical trials. In addition, early intervention could offset the need for resource-intense GDM management or insulin therapy.